Digital tone generator system for electronic organ employing a single master oscillator

ABSTRACT

For use in electronic organs and the like, an electronic circuit for generating a number of signals, the frequencies of which may correspond to the notes of the musical scale, comprises a single master oscillator producing an alternating signal coupled to a harmonic pulse frequency generator producing a number of harmonically related pulse frequency outputs which are selectively connected to summing means, each summing means producing a single output frequency which corresponds to a note of a musical scale. Twelve summing means may be connected selectively to produce the twelve notes of a musical scale.

11,51 14s]- Nov; 7,1972

1 1541 TDQIIGITAL TONE GENERATOR SYSTEM- FOR ELECTRONIC ORGAN 1EMPLOYING ASINGLE MASTER 1 OSCILLATOR 1 1 I v [72] Inventor: John RayHallman, Jr., Green Banlc,

' W. Va. 24944: I 1

221' Filedi May 19,1971

211 Appl. No.:144,874

52] -U.s c1.... ...s4/ 1 .0 1,-s4/1'.04,84/111,

. V .84/1. 19, 84/1.22,84/124 s1 1 11.c1...; .'.G1 0h1/00 [58] Field ofSearch ......84/1.01, 1.03,1.11,1.17,

84/125, DIG.11, 1.19; 307/225, 226; 1

I FOREIGN PATENTS OR APPLICATIONS 1' 1,213,210 3/1966, Germany;..s4/1.03

OTHER PUBLICATIONS I Richard Phillips, Many Digital Functions 'Can BeGenerated, Electronic Design 3, Feb. 1 1968 pages PrimaryExaminer-Richard B. Wilkinson 7 Assistant Examiner-U. Weldon [571ABSTRACT For use in electronic organs and the like, an electroniccircuit for generating a number of signals, the frequem cies of whichmay correspond to the notes of the musi- 1 cal scale, comprises a singlemaster oscillator produc- 331/5l,53 ing an alternating signal coupled toa harmonic pulse i frequency generator producing a number of harmoni-[56] References Cited cally' relatedpulse frequency outputs which areselec- 1 1 tively connected to summing means, each summing I D STATESPATENTS 1 means producing a single output frequency which cor- 3 509 4544/1970 1 Gossel 84/1 i X responds to a note of a musical scale. Twelvesumming 1 means may be connected, selectively to produce the 3,617,90111/19 71 Franssen ..84/1.01 X twelve notes of amilsical Scale 3,590,1316/1971 Reyers.....-... V ..84/1.03 I 1 3,601,518 8/1971, l lill;...84/,l.l.9 6 Claims, 7 Drawing Figures r CRYSTAL 1 (Y --B|, 822E311DIGITAL (W PULSE A. cmrsm. HARMONIC {V FREGUFNc YG G1 1?." MASTER I u 1OSCILLATOR PULSE SUMMING q 1 I Fm CRYSTAL GE'NERATGR k5 GATES F, MASTERa B OSCILLATOR F 2 KP V D11.

. k 17. VOLTBGE p I P 56 1 14 com-amen (D 1 -M F a lfsiilfils k ANALOG 1INHIBIT VOLTAGE CONTROL cowraou INPUT 'mPuT r {m nim #1 m 12 MASTER YOSCILLATOR I MAST-ER \4- CONTROLLED K I.

\'NPuTf 3702.370 "sum 1pm I -f n I D IGlTALI PULQE A HARMONICFREQumcY%C-}fl MASTER oscuu'nma CRYS AL PULSE K 1 summmo RYSTAL Q 6ENEATQ LVFE M' Q ra vomoa ANAL I I QYIAIIHIQBIT -voLTn6E I 1 CONTROLCONTROL. mpur INVENTOR" 61w www DIGITAL ,TONEGENERATOR SYSTEM FOR-1 I'ELECTRONIC.ORGAN EMPLOYING A SINGLE- 5 MASTEROSCILLATOR- v .The,presentinvention relates generally to electronic organs and moreparticularly to the p'roductionof the supersonic or high f requencysignals corresponding .to

\ the twelve notes of'the'musical scale used in someelectronicorgan'systems. v v t ln 'the usual tone generator of anelectronic-organ,an

} array of 12 master oscillators is provided which operate.

at. high audio-or supersonic frequencies. These oscillators each drive achain of octave dividers producing the 1 the organas will becomeapparent after the invention is completely described. Also, thepulsewidths produced bythe'DHPG' are very narrow The pulse width is chosen tobe equal-to about one-half the period of the frequency that resultsfrom'thearithmetic sum of the values of all the frequency; outputs ofthe DHPG. The

' description .of the ".pulseffrequency summing gates should make thisclear. lo the invention the. pulse octaves'of the notes. In accordancewith thepresent invention on .theotherhand, only one master oscillatoris required. This oscillator iscoupled a digitallhar; monic pulsegenerator (DHPG): that produces a. multiplicity of harmonicsof themasteroscillator. The harmonics produced are fixed by the'organ designerand I I may be chosen for convenience of design as well as economy. Thevarious harmonics produced in a-DI-IPG are selectively-summed in adigital 'or' gatepulse summing scheme to produce the l2 frequencies of.the

notes of amusical scale,the octave of which is chosen I by the designerbut i's'usu'ally a high octave in theupper range. of human hearingability. It may.,-'actually, be higher than the range ofhuman hearingand usuallyis.

Each of these notefrequencies is connected to'a'con- I ventional octavedivider chain producing the, lower octaves of. each note. Thus, thewhole gamut of note frequencies maybe produced.

j The whole system is digital in nature and hence, is well defined. thescience of large scale integration in packaging circuits advances,'itwill soon bepossible to v package. the entire integrated circuit into asingle chip with a multiplicity of leads connectingto the mechanicalparts of the organ. So the entire digital electronic circuitmay bepackaged into anintegratedfcircuit 'allowinggreat economy in buildingelectronic music in-.

struments. Thisinvention of thefpresent application also improves thetuning stability of the organ since only one oscillator is requiredwithall'other frequenciesbeing digitallyrelated tothe one masteroscillator.'

3, In further accordance with. I frequency" summing gates (PFSG) areprovided to' selectivelysum theoutputs of-toDI-IPGf ThePFSG performs anarithmetic addition of the -Dl-IPG outputs similar to the followingsimplifiedexample. ,If we have a DHPG to whichhas been connected anoscillator at a frequency of 8 hertz and further, the DHPGis binary so Ithat it'producesthe harmonic pulse frequencies of 4 hertz,- 2 hertz, andl hertz; then we may obtain the.

frequency of hertz'by using-a digital or gate to add thetwo, DI-IPGoutputs of '1 ,and'4 hertz. In fact,we may 3. obtain anyofthefrequencies l, 2, 3, 4, 5,6, or7'hertz thisway; Notethat 7; hertz is lhertz less thanlthe oscillator frequency of 8 hertz. One hertz is equalto the least significant bit of the DI-IPG where each of the outputfrequencies of the DI-IPQ are referred to as bits. It can be seen thatthe choiceof theDI I'PGoutput pulse width of one-fourteenth second isoptimumbecause this provides an approximately 50 percent duty factor atthe PFSG output for 7'hertz which further assures that no DIIPG outputpulses occur at the same instant of time which would cancel pulses,there by causing freq'uencyerrors. For the case where the tone generator system operates from the output of a, voltage controlled oscillatorthe pulse width mentioned above should be selected" after consideringthe. highest frequency output of the voltage controlled oscillator. In

order that this invention. produce the 12 frequencies'of the notes ofthe scale, it'is necessary that theD I-IPG have more than three bits."The actual-quantity is dependent onthe frequency of themasteroscillaton'the type of cooling or harmonic relationship of theoutputs of theDI-IPG, and the precision of the musical note i Inaccordance withtheinvention, a master oscillator I is provided with afrequency-(Fe) several times higher than thehighestnote played on theorgan. Fo depends on several factors, namely; ho is chosen to minimizethe required structure of the pulse summing gates, Fo

, must be chosen high enough above the highest note on the organ so thatthe unwanted harmonic content (phase jitter) of this note is minimizedto an acceptable level, and other factors, all of which become moreapparent after consideration of the detailed description of oneembodiment of thisinvention. v I In further accordance with theinvention, a digital harmonic pulse generator (DHPG) is provided 'toproduce the pulse frequencies. Inthe present invention, the DI-IPGproduces 12 frequencies. This is pure coincidence with the fact thatthere are 12 notes in the I must be in the range of the oscillatorcapability, Fo

frequencies produced. Thisis againa costvs precision tradeoff. The typeof coding mentioned above is concerned with the digital codingschemesused in any-conventional digital systems design. Any type coding may beemployed but after design considerations it will be found that certaincoding schemes are better than others affording more precision at lesscost. Some exainples of coding that may be used are 8421 binary, codeddecimal, 5411, 5211, l 1 l 1, etc. In the embodiment of the inventionpresented herethe coding used is 8421 binary which is easily generatedfrom a digital bimusical scale, but any other quantity of pulsefrequencies'could be chQsemThere is an optimum quantity thatis a tradeoff between economy and precision of I frequency of the musical notesthat are produced in this 1 organ tone generator system. The more pulsefrequencies produced by the DI-IPG, the more precise will be the musicalnotes and also the more'e'xpensive will be are in the form of phasejitter and very narrow pulses in I the conventional sense. Theseeffectsare divided at the 3 same ratio as frequency is divided in flipflops and octave divider systems. In view of this effect it may bedesirable to increase the frequency of the master oscillatortocompensate for a number of stages of division if employed before makingavailable the highest octave outputs from the conventional octavedividers. The

lower octaves are further divided in frequency and hence will contain aneven smaller percentage of unwanted harmonics. This organ system employs12 chains of octave dividers in one application, one for each noteofmusical scale. Essentially the invention is intended to replacethe 12master oscillators usually connected to the octave dividers found inconventional organ designs. The number of stages in the octave dividerchain depends on the overall range that the organ is to have. The gamutvof notes of the organ are found at complete organ tone generationsystem that has as it reference requirement, although not limited to,one master oscillator and that is capable of generatingthe l2 supersonicnote frequencies that are usually produced by a set'of 12 masteroscillators in most conventional systems.

ltis another object of theinvention to provide a vibrato effect withheretofore unattainable wide frequency modulation range of many octavesby voltage control of the master oscillator when a voltage controlledoscillator is employed'instead of a crystal controlled oscillator.

It is a further object of the invention to provide switch selectableinstrument key selection. Organs and pianos usually are tuned in the keyof C. But with this inventionby providing more crystal oscillatorsselected by switch or some other variable oscillator reference,

the organ may be tuned to any other musical key quite easily without thenecessary tuning job that would otherwise'be required.

- by just turning a knob that controls the potential applied to thecontrol terminal of a voltage controlled master oscillator. I

It is a further object of the invention to provide for easily andselecting tuning the organ to other. temperaments such as the just,mean, or pythagorean scales. This embodiment of the invention is mainlyshown in this patent application adjusted for the equal temperamentscale, however.

The above and still further objects, features and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed description of one specific embodiment thereof,especially when taken in conjunction with the accompanying drawings,wherein;

FIG. 1 is a block diagram of asystem for generating the 12 high audioor' supersonic frequencies corresponding to the notes of the musicalscale. I f n FIG. 2. is a digital harmonic pulse 'gie'neratortDI-IPG)providing 12 harmonically related pulse frequencies, in the system ofFIG. 1. j I, t I

FIG. 3 is a group of 12 pulse frequency summing gates for producing the12 high audio or supersonic musical note frequencies when connected tothe outputs of the Dl-IPG of FIG. 2, in thesystem of FIG. 1.

FIG. 4 is a simplified. alternate construction of a digitalharmonic-pulse generator (DI-IPG) coupled to a pulsefrequency summing.gate (PFSG); "that. were shownin FIGS.2and 3.

FIG. 5 is a timing diagram sequences of some of the signals in thecircuit of FIG. 2.

FIG. 6 is a timing diagram showing the timing sequences of :signalspresent in the simplified example ofFIG.4: w I

FIG. 7 is an optional'4 octave dividerthat may be employed to improvethe purity of the supersonic note frequency outputs of the pulsefrequency'summing gates (PFSG).

Referring now to the accompanying drawings, in FIG. 1, the blocks ll,l2, l3, and 14 are all oscillators "nroducing squarewave outputs 15, 16,17', and 18 compatible with the driving requirements-of the type ofdigital logic circuits employed in this embodiment of the presentinvention. In all-examples of the present invention the logic used istransistorrtransistor logic (TTL) integrated circuits. This is not alimitation since any form of logic circuits may be employed in thedesign of the invention. In conventional TTL circuits the followingdefinitions prevail. A logic 1 is true and a voltage level ofapproximately plus 5 volts, whereas a logic 0 is false and is a voltagelevel of approximately ground potential. A plus edge is a logictransition from 0 volts to plus 5 volts, whereas a minus edge is a logictransition from plus Sto 0 volts. A plus pulse is comprisedlof a plusedge followed after'a time interval (pulsewidth) by a minus edge back toground potential, whereas a negative pulse is comprised of a minus edgefollowed after a time intervalby a plus edge back to plus 5 volts level.a

The four oscillators areshown switch selectable to allow the organ'to betuned to a different musical key simply by changing a selector switch.In actual application there may be as many oscillators as the builderdesires but there must be at least one oscillator since this is thereference to which all musical notes produced by the invention arereferenced. So, with the proper oscillator frequencies chosen, threedifferent musical keys would be allowed by the oscillators 11,

ing a vibrato range of many octaves heretofore not v possible with otherorgan tone generator systems. In

showing v the timing i fact by playing achord on the organjand thenvarying the potential "on the control input of the voltage controlledoscillator '14 ina selectiveway music compristo the referenceoscillator. For this example of the invention the outputs areplus pulsesthat follow the binary progression whereby Y is one-halftheoscillatorfrequency andX is one-fourth'the oscillator frequency and so on until Lis 1/4096 0f the reference oscillator frequency. The digital harmonicpulse generator circuit number of special has 19 asI.,M',N,P,R,S,T,U,V,W,X,Y are harmonically related I may be any one ofseveral types of devices without departing fromthe true spirit of theinvention.

These pulse frequencies are thenselectively summed by the pulsefrequencysumming gates 21,'to produce the supersonicpulsetraini frequencies ofthe'musical notes of thescale. These pulse trainfrequency outputs areinharmonic since they contain much phase jitter as well as being verynarrowpulses.= Theseoutputs maybe made more pure by dividingwith digital'flip flop circuits before allowing any outputs to reach thelistener.The circuit of FIG. 7 may be used forthis purpose and is optional as howmany stages of division to employ. More stages of division will producemore purity of the outputs.

In FIG. 7 the input is C12, for example connected from'Cl2 of FIG. 1.Thedivide' by two circuits26, are flip flops, four stages of which willproduce C8 at the output. It may be desirable to increase the masteroscillator frequency by a factor of'l'6 thereby'raising the input to C16following the nomenclature. The output of the circuit of FIG. 17 willthen be C12, allowing the full musical range of theorgan. Theseoutputsmay then be connected to conventionaloctave divider and harmonicprocessing tone circuits to providethe gamut of A timing diagram showingthe timing sequence of some of the signals present in the digital,harmonic pulse generator of FIG. 21is shown in FIG. 5. Notice that thetransitions of 23, 24 and 25 occur during negative transitions of theclock input 19. Also'note further that pulse trains W, X, and Y occur atplus edges of-25, 24, and"23, respectively. This must be arranged thisway to assure that no two one-shots are triggered at the same instantwhich'wo'uld cause their outputs to occur in coincidence,thereby'causing cancellation of some pulses being summed by'the summinggates-rendering frequency summing errors; The important thing is that notwo pulses be allowed to occur at the same instant of If a digital orgate has'inputs connected to Wand Y then with amasteroscillatorfrequency of 8' hertz, a frequency of 5 hertz is presentat the output of the-or gate since the frequency of Y undertheseconditions-is 4 hertz and W is l hertz. The pulse frequencies of W and Yare sumed by theor gate. Z in FIG. 5 shows what the or gate output lookslike in time sequence..Note.

that the pulses are not evenly spaced but exhibit a phase jitter.Because of this effect musical notes produced directly from a systemsuch as this are inhar- T monious, since many harmonics not correctlyrelated .to the fundamental are produced. However, this phase jitter mayeasily be'reduced by dividing through flip flops and increasing themaster oscillator frequency to compensate for the division ratio ofseveral flipflops.

FIG. 3 shows a group of 12 pulse frequency summing gates 50 that may beemployed in item 21, FIG. 1 to process the outputs of the DI'IPG toproduce the high audio or supersonic frequencies corresponding to 12notes within a single octave range for the organ. The

operation of these or gates is identical to that of the or gate in theprecedingparagraph "except that more inputs are present.L,M,N,P,R,S,T,U,V, W,X,,and Y are v inputs to the gatesfrom the DI-IPGof FIG. 2, the pulse frequencies of which are tabulated in table 1. ITABLE 1 g 1' a Fo=780.8 frequencies in hertz Y=390.4

S=6.1 R=3.05 P=l .525 N=.7625 M=.38 125 L=. 190625 V The frequenciesshown result if the master oscillator frequency E. is set equal to 780.8hertz. These frequen- The flip flop outputs drive monostableone shotsthat trigger on different edges from the flip flops namely the plusedges so that onplus transitions of the outputs of the flip flops thereare pulses present at L,M,N,P,R,S,T,U,V,W,X, and Y. These are thepulsefrequency outputs of thedigital harmonic pulse generator.

cies may be selectivelyv summed in certain ways to produce theproperfrequencies of the 12 notes of the equal tempered musical scale,approximated to an average accuracy of 0.0953 125 hertz. Table 2 is atabu lation of the exact frequencies of the notes of the musical scaleof equal temperament. The summingcom binations are shown on the rightside of the table. To

obtain the note G for example we, add Y and as indicated by a l intherespective columns. The note will same.

7 or minus 0.0 hertz. The error will not be noticed by the listener.Accuracy and system costmay be reduced by reducing the number offrequencies generated by the Dl-IPG. More accuracy may be obtained byincreasing TABLE 2 For F 780.8 hertz and all frequencies specified inThese values of frequencies and combinationsshown in Tables 1 and 2 wereobtained from a computer program that minimized pulse frequency summinggate structure vs.- F0 within a small range of F0. It is obvious that abetter computer program will generate more combinations for summingpulse frequencies at different F0 frequencies and that this does notdepart from the scope and spirit of the present invention.

The inhibits inputs to the gates of FIG. 3 allow them to be inhibited bylogic control signal while another gate or set of gates are enabled. Inthis case all gates producing C12 for example are coupled to the octavedividers and likewise the other eleven may be coupled to the outputs inthe same manner. The feature allows special effects and changabletemperaments at will. The inhibit input in FIG. 1 serves the samepurpose and in-fact, is the same where the inhibit inputs of each gatein'a set of 12 are grouped to this input. A logical high level to thisinput will inhibit the operation of the PFSG in FIGS. 1 and 3. It isobvious that by computer program or other means a set of pulse frequencysumming gates may be designed to produce the just, mean, or pathagoreantemperament scales.

A simplified alternate system for producing one frequency of 5 hertz isshown in FIG. 4. In this example a gating scheme is employed instead ofthe analog monostable one shots to produce the pulses. The operation issimilar to the previous example and is included for clarity as well asto demonstrate that there are a multiplicity of ways of building thepresent inven- While I have described and'illustrated one or twospecific embodiments of myinvention, it will be clear that variations ofthe details of construction which are specifically illustrated anddescribed may beresorted 5 to without departing from the" true spiritand scopeof the invention as defined in the appended claims.

An exact circuit diagram of a modelof the invention along with adescription is on file at the" United States I Patent Office and isdisclosure document number 5076 10 filedMayl4,l97l. -WhatIclaim is:

l. A tone generating system for an electronic organ comprising a masteroscillator means producing a s'quarewave output connected to a-singledigital harmonic pulse generating means producing anumber of pulsefrequencies connected to a plurality of pulse frequency summing means,eachpulse frequencomprises a plurality of master oscillators set atdifferent frequenciesthereby allowing the organto be tuned by selectorswitchinstantly to different musical keys by selecting correspondingmaster oscillators.

2. The combination according toclaim fwherein said master oscillatormeans comprises a voltage controlled oscillator allowing the musical keyto which the organ is tuned to be altered' by varying the potentialapplied to the voltage control input of the master oscillator, thusallowing the organ toproduce a multiplicity of special effects. I

3. The combination accordingto claim twherein said digital harmonicpulsegenerating meats comprises a chain of cascaded digital flip flopcircuits, the outputs of which are coupled to monostable one shotsproducing the pulse frequencies. r

4. The combination according to claim 1 wherein said digital harmonicpulse generating means comprises a chain of cascaded digital flip flops,the outputs of which are coupled to gating means producing the pulsefrequencies.

The nesqqrs ia F9 1a 19. ,wl s: a

' number of ahai'fisbr flip flops of N stages each are connected to eachpulse frequency summing means output '50 (and the conventional octavedivider chains) and further increasing the master oscillator frequencyby a factor of 2" to compensate for the flip flop division ratios thusreducing the undesirable harmonic content of the musical notefrequencies appearing at the out- I tion. The oscillator 31 output is an8 hertz squarewave jipqtspf Said flip flop di e Chains.

connected to a chain of three flip flop divide by twos 26. The inverters33 invert the sense of the logic signals connected to them. The andgates 32 produce 1, 2, and 4 hertz from top to bottom respectively. theoutputs 39 and 41 are summed in or gate 34 to produce the 5 hertz output42. The and gate output 40 is not needed and hence, is not used toproduce 5 hertz. A timing diagram for the signals present in FIG. 4 isshown in FIG. 6. Note that none of the pulses of 39, 40, and 41 occur atthe same instant of time.

6. The combination according to claim 1 wherein said master oscillatormeans comprising a crystal oscillator, saidhigh pulse frequency, eachconnected to flip flop divider chains producing audio frequencies towhich other types of musical instruments may be tuned thus allowing areference for the tuning pur-

1. A tone generating system for an electronic organ comprising a masteroscillator producing a squarewave output connected to a single digitalharmonic pulse generating means producing a number of pulse frequenciesconnected to a plurality of pulse frequency summing means, each pulsefrequency summing means connected to selected pulse frequency outputs ofsaid digital harmonic pulse generating means whereby each pulsefrequency summing means produces a single high pulse frequency at itsoutput that is equal to the sum of the selectively connected outputs ofsaid digital harmonic pulse generating means.
 2. The combinationaccording to claim 1 wherein said master oscillator comprises aplurality of master oscillators set at different frequencies therebyallowing the organ to be tuned by selector switch instantly to differentmusical keys by selecting corresponding master oscillators.
 3. Thecombination according to claim 1 wherein said master oscillatorcomprises a voltage controlled oscillator allowing the musical key towhich the organ is tuned to be altered by varying the potential appliedto the voltage control input of the master oscillator, thus allowing theorgan to produce a multiplicity of special effects.
 4. The combinationaccording to claim 1 wherein said digital harmonic pulse generatingmeans comprises a chain of cascaded digital flip flop circuits, theoutputs of which are coupled to monostable one shots producing the pulsefrequencies.
 5. The combination according to claim 1 wherein saiddigital harmonic pulse generating means comprises a chain of cascadeddigital flip flops, the outputs of which are coupled to gating meansproducing the pulse frequencies.
 6. The combination according to claim 1wherein a number of chains of flip flops of N stages each are connectedto each pulse frequency summing means output (and the conventionaloctave divider chains) and further increasing the master oscillatorfrequency by a factor of 2N to compensate for the flip flop divisionratios thus reducing the undesirable harmonic content of the musicalnote frequencies appearing at the outputs of said flip flop dividerchains.
 7. The combination according to claim 1 wherein said masteroscillator comprising a crystal oscillator, said high pulse frequency,each connected to flip flop divider chains producing audio frequenciesto which other types of musical instruments may be tuned thus allowing areference for the tuning purposes of other music instruments.